Reactors in general and fluidized bed reactors in particular have been used to remove and recover phosphorous from solutions such as wastewater and process water. Aqueous solutions from some sources contains significant concentrations of phosphorus, often in the form of phosphate. Such aqueous solutions may come from a wide range of sources. These include sources such as leaching from landfill sites, runoff from agricultural land, effluent from industrial processes, industrial process water, municipal wastewater, animal wastes, phosphogypsum pond water, and the like. Such aqueous solutions, if released into the environment without treatment, can result in excess phosphorus levels in the receiving waters.
Various phosphorus removal and recovery technologies exist. Some of the technologies provide fluidized bed reactors for removing phosphorus from aqueous solutions by producing struvite (MgNH4PO4.6H2O) or struvite analogs or other phosphate compounds in the form of crystals. Struvite can be formed by the reaction:Mg2++NH4++PO43−+6H2O⇄MgNH4PO4.6H2O
Koch et al., fluidized bed wastewater treatment, U.S. Pat. No. 7,622,047, describes example reactors and methods that may be applied to remove and recover phosphorus from aqueous solutions.
A difficulty sometimes exhibited in crystallization reactions is that the sizes of particles produced by the reaction may not be as desired. For example, under certain operating conditions, a reactor may produce very tiny crystals (“fines”) where larger crystals are desired. Crystal sizes are affected by a wide range of factors including flow conditions, chemical composition, temperature etc.
References that describe various crystallization processes include: U.S. Pat. Nos. 8,245,625; 7,942,939; WO2006082341; U.S. Pat. Nos. 6,946,572; 6,364,914; WO9837938; U.S. Pat. Nos. 4,666,527; 3,419,899; 2,209,019; 4,159,194; 4,263,010; 5,124,265; 6,660,049; 5,663,456; AU2004320909; WO2012022099; WO2012134255.
There remains a need for effective apparatus and methods for removing and recovering dissolved materials from solutions. There remains a particular need for effective methods and apparatus suited to making large particles of marginally soluble substances such as struvite, struvite analogs and calcium phosphate.